It is well known to employ dies and the like for forming metal parts as seen for example in U.S. Pat. Nos. 2,526,489 to Liddicoat, 3,038,220 to Saives, 3,286,502 to Cogan, 3,583,198 to Drallmeier and 3,896,651 to Starkier. Saives U.S. Pat. No. 3,038,220 relates to pressure die casting and is not relevant to the making of forged spiders.
Liddicoat U.S. Pat. No. 2,526,489 teaches the use of a forging billet and die for making drill bits.
Cogan U.S. Pat. No. 3,286,502 teaches the use of a forging billet with pressure exerted on opposite ends of the billet to extrude the billet through one or more side openings of a die to form air foil sections.
U.S. Pat. Nos. 3,583,198 and 3,896,651 teach extrusion die forming of universal joint spiders. The U.S. Pat. No. 3,583,198 supports one end of a forging billet in a die and exerts force on the other end of the billet to extrude the billet into four equally spaced die openings. The U.S. Pat. No. 3,896,651 supports the bottom of a forging billet and exerts force on the top end of the billet to extrude it between base columns to form a preform spider which is then further shaped in a forming die. The first forging step is said to reduce the amount of flash in the second step and hence reduce the amount of material used. The spiders produced by these patents have different grain structures as is detailed later.
The conventional (and heretofore accepted to be the best) method for forming a cruciform journal forging such as a universal joint spider forging prior to this invention and in wide use today is by hammer or press forging utilizing moving die halves to deform a heated billet and force the metal to conform to the shape of the die cavities. This movement of metal is generally accomplished in two or more stages in order to minimize the amount of material which cannot be retained in the final cavity. This wasted material, called "flash", is necessary to serve to restrict the movement of material away from the die cavities. After the forming is completed, the flash is trimmed from the finished part and becomes scrap. The amount of material lost as flash is generally 20-30% of the original billet weight. The trimming operation introduces another dimensional variable which, when combined with the tolerances needed for die wear and mis-match of die halves, results in general industry standards of .+-.0.030" for most dimensions. The grain flow lines in the finished part will depend on the orientation of the original billet but, because of the flash formation, some of the lines must necessarily terminate at the trim line on the sides of the finished part.
The method of this invention solves the aforementioned problems and produces a more torque resistant product. A universal joint spider forging produced by the invention is flashless and hence is produced without the waste of any of the starting material. With the close manufacturing tolerances obtainable, and the absence of trimming, the forging produced by the invention can be held to a tolerance of .+-.0.005" in most dimensions, resulting in a part which can be machined faster with longer cutting tool life and with less scrap caused by alignment problems in the holding fixtures while machining. The grain flow lines in the finished forging have no terminations except on the ends of the legs and flow smoothly through the body from one leg to each adjacent leg for improved torque handling capabilities.
A forging produced in accordance with the invention can be subjected to further forming by hammer or press forging without substantial loss of the above benefits.